Responses of the trypanosome surface to drugs, metabolically active substances, host tissues, cells, immunoglobulins and perhaps hormones are critical in relationships between thse parasites and their hosts. The role played by the majro variant surface coat glycoprotein (VSCG) in antigenic variation and immune evasion is well established in laboratory infections with African trypanosomes. The moleculr basis for antigenic variation is beinning to be understood. The long-term objective of this proposal is to determine what role(s) the minor surface membrane glycoproteins (mSMGs) play in interactions between trypanosomes and their hosts. During the period of current support, we identified a series of four mSMGs in whole cells and in membrane enriched fractions of Trypansomoa brucei. These polypeptides along with the VSCG are related by association wit the cell membrane and susceptibility to surface iodination. They are distinguished by the molecuar weights. All appear to be N-linked mannose-containing glycopeptides, and some, those with Mr=130,000, 100,000 and 76,000, are also phosphorylated. We have selected two of these for intense study as model system: 1) the 76,000 Mr glycopeptide, easily solubilized from the cell surface and 2) the 130,000 glycopeptide, an apparent integral membrane protein. Using these two mSMGs, we are refining our biochemical and immunochemical approaches and will apply them to a study of function and relationships among the minor and major surface glycoproteins. In the isolation and characterization of these SMGs our approach is 1) to use triple-cloned variants of Trypanosoma brucei YTats, 2) to produce monospecific polyclonal rabbit antiserum to SMGs, 3) to generate panels of monoclonal anti-SMG hybridoma antibodies, 4) to use antibodies to selectively study the location and function of SMGs on whole cells and membrane vesicles, 5) and to construct operatonal maps of these proteins by comparative analysis of cloned variants of slender trypomastigotes, intermediate and stumpy forms, and 27 degrees C culture forms. the characteristic occurrence of relapsing infections in African trypanosomiasis in attributed to changes occurring in the antigen structure of the major SMG. If the mSMGs are rather less remarkable in their ability to change, then they will likely provide novel clues in the diagnosis and control of trypanosomiasis.